#include <iostream>
#include <vector>
using namespace std;

class Solution
{
public:
    int singleNumber(vector<int> &nums)
    {
        int a = 0, b = 0;
        for (int num : nums)
        {
            tie(a, b) = pair{(~a & b & num) | (a & ~b & ~num), ~a & (b ^ num)};
        }
        return b;
    }
};

int main()
{
    cout << "Code137" << endl;
    Solution s;
    return 0;
}